c++ - LCOV 在函数末尾分支

Question

这个函数的末尾有哪些分支。我该如何覆盖它们？

Answer 1

您正在观察 gcc 生成的用于销毁静态存储持续时间(全局)变量的代码。

您的覆盖显示函数 foo 已被输入 3 次，但是范围末尾附近的计数器显示代码已执行 8 次，包括您查询的分支。

现在您必须考虑编译器将头文件放在翻译单元中并且 gcov 不会完全按照原样查看您的代码，而是将其作为汇编指令的控制流图，分支作为图的边缘.

因此，lcov html 输出中的“foo 作用域结束”实际上并不是 foo 方法作用域的结束，而是 foo 之后包含的所有内容 以及整个翻译单元，包括销毁已在头文件中声明的全局变量。

header 本身并未包含在问题中，但即使是 gcc 生成的最基本的 __static_initialization_and_destruction 程序集也包含许多分支。

请注意，您可能已经包含全局变量，也可能没有 - gcc 仍可能为每个翻译单元生成此代码。

---

查看gcov的底层输出:

function _Z3fooi called 1 returned 100% blocks executed 50%
        1:    4:int foo(int x) {
        1:    5:    if (x==1) {
branch  0 taken 0% (fallthrough)
branch  1 taken 100%
    #####:    6:        std::cout << "foo" << std::endl;
call    0 never executed
call    1 never executed
    #####:    7:        return 0;
        -:    8:    }
        1:    9:    return 1;
function _GLOBAL__sub_D__Z3fooi called 1 returned 100% blocks executed 100%
function _GLOBAL__sub_I__Z3fooi called 1 returned 100% blocks executed 100%
function _Z41__static_initialization_and_destruction_0ii called 2 returned 100% blocks executed 100%
        6:   10:}
call    0 returned 100%
call    1 returned 100%
branch  2 taken 50% (fallthrough)
branch  3 taken 50%
branch  4 taken 100% (fallthrough)
branch  5 taken 0%
        -:   11:

然后查看生成的程序集，修剪以阐明要点:

        ...
        ret
        .seh_endproc
        .def    _Z41__static_initialization_and_destruction_0ii;        .scl    3;      .type   32;     .endef
        .seh_proc       _Z41__static_initialization_and_destruction_0ii
_Z41__static_initialization_and_destruction_0ii:
.LFB978:
        ...
        mov     QWORD PTR __gcov0._Z41__static_initialization_and_destruction_0ii[rip], rax
        cmp     DWORD PTR 16[rbp], 1
        jne     .L5                                 <-- BRANCH
        mov     rax, QWORD PTR __gcov0._Z41__static_initialization_and_destruction_0ii[rip+8]
        add     rax, 1
        mov     QWORD PTR __gcov0._Z41__static_initialization_and_destruction_0ii[rip+8], rax
        cmp     DWORD PTR 24[rbp], 65535
        jne     .L5                                 <-- BRANCH
        ...
.L5:
        cmp     DWORD PTR 16[rbp], 0
        je      .L6                                 <-- BRANCH